The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art to the present invention.
Stem cells are cells having the ability to self-renew and divide to an unlimited extent and to differentiate under suitable circumstances to form different types of cells. Embryonic stem cells (ES cells) are stem cells established from early embryos which can be cultured over a long period of time while maintaining pluripotent ability to differentiate into all kinds of cells existing in living bodies. By contrast, somatic stem cells are any cell which is found in a developed organism that has the ability to divide and create another cell like itself and also divide and create a cell more differentiated than itself.
Thomson et al. (U.S. Pat. No. 5,843,780; Proc. Natl. Acad. Sci. USA 92:7844, 1995) were the first to successfully isolate and propagate pluripotent stem cells from primates. They subsequently derived human embryonic stem (hES) cell lines from human blastocysts (Science 282:114, 1998). Gearhart and coworkers derived human embryonic germ (hEG) cell lines from fetal gonadal tissue (Shamblott et al., Proc. Natl. Acad. Sci. USA 95:13726, 1998; and U.S. Pat. No. 6,090,622). Both hES and hEG cells have the long-sought characteristics of pluripotent stem cells, i.e., they can be cultured extensively without differentiating, they have a normal karyotype, and they remain capable of producing a number of important cell types.
Induced pluripotent stem (iPS) cells are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell. Yamanaka et al. transfected mouse fibroblasts with four genes (Oct4, Sox2, c-Myc, Klf4) to obtain iPS cells in 2006. Subsequently, iPS cells were created from human adult somatic cells. (Takahashi et al. Cell, 131:861-872 (2007); Yu et al. Science, 318:1917-1920, 2007).
The field of regenerative medicine encompasses therapies designed to aid the repair, replacement, or regeneration of damaged cells, tissues, or organs. Stem cell-based therapies have the promise of treating a variety of health conditions including Alzheimer's Disease, Parkinson's Disease, stroke, spinal injuries, heart attack, renal failure, osteoporosis, type I diabetes, multiple sclerosis, rheumatoid arthritis, burns, and wounds. However, the progress of such therapies has been hindered by a range of factors including the possibility of immune rejection of ES cells derived from a donor who is immunologically incompatible with the recipient.